The present invention relates to levitation devices and methods and more particularly to the levitation or suspension of a permanent magnet in a magnetic field produced by another magnet (either permanent or electromagnetic) using no mechanical restraints or supports.
Magnets, both permanent magnets and electromagnets, find a wide variety of uses, both practical and as entertainment devices. The poles of magnets have been named the north pole and the south pole, the north pole being the one that points northward in the Earth""s magnetic field, i.e., the magnetic north-seeking pole. It is, of course, well known that like poles, i.e., two north poles, repel one another and unlike poles, i.e., a north pole and a south pole, attract one another.
This phenomenon has been used to levitate one magnet above another and offers the possibility of substantially reduced friction. Magnetic levitation of trains, for example, is one practical application of the phenomenon. However, in such a levitation application, highly sophisticated control devices are required for controlling the magnetic fields of electromagnets to overcome the inherent instabilities of the repulsion forces of two like magnetic poles. In a simple levitation system wherein one pole of a first permanent magnet is attempted to be suspended above a like pole of a second permanent magnet, the inherent instability of such a system results in the flipping over of the first magnet so that the unlike poles attract and are brought together into a stable configuration.
A number of simple levitation systems have been devised which employ specially configured permanent magnet arrangements intended to minimize the instability associated with magnetic levitation. In U.S. Pat. No. 2,323,837 to Neal, for example, there is disclosed a magnetic system having a base magnet comprising a circular disk in which a first plurality of cylindrical magnets is disposed in a circular array about the axis of the circular disk. An upper magnet member comprises a spherical segment in which a second plurality of cylindrical magnets is disposed in a circular array of smaller diameter than the diameter of the circular array of the base magnet. The first plurality of magnets is disposed with like (north) poles and longitudinal axes directed vertically upwardly or inclined slightly toward the axis of the circular disk. The second plurality of magnets is disposed with like (north) poles and longitudinal axes directed vertically downwardly or inclined at the same inclination as the first plurality of magnets. This arrangement of the base magnet is said to produce an inverted magnetic field cone which embraces the smaller diameter magnet field of like polarity of the upper magnet and thereby is said to stabilize the levitation system.
U.S. Pat. No. 4,382,245 to Harrigan discloses another simple magnetic levitation system which utilizes a dish-shaped lower magnet to magnetically support or levitate a magnetic top spinning coaxially above the lower magnet. The dish-shaped or concave surface of the lower magnet is said to produce radially inwardly directed lines of magnetization which, together with the gyroscopic effect of rotation of the magnetic top, provide stabilization ,of the levitation system. The Harrigan patent discloses another embodiment in which stabilization is said to be provided by a combination of the concave lower magnet surface and a pendulum effect resulting from a non-magnetic mass supported below the lower magnet on an arm extending from the upper magnet through a central bore in the lower magnet. Other embodiments are disclosed in which the lower field is not provided by a dish-shaped magnet but is provided by a plurality of cylindrical magnets arranged similarly to the arrangement of the aforementioned Neal patent.
The present invention is directed to a magnetic levitation device and method that accomplishes stable, unrestrained levitation of one magnet above another magnet by utilizing a previously unrecognized characteristic of the magnetic field above a magnetized surface and by incorporation of a rotational motion of the levitated magnet. Although the magnetic levitation device of the present invention may have other applications not specifically described herein, it is intended to provide an educational or amusement device that may be readily manufactured at low cost and operated simply, reliably and reproducibly with minimal instruction.
In our prior copending application U.S. patent application Ser. No. 08/197,845 filed Feb. 17, 1994, now U.S. Pat. No. 5,404,062, the complete disclosure of which is incorporated herein by reference, we disclosed a magnetic levitation device and method. The levitation device comprises a uniformly magnetized flat or substantially planar magnetic base above which is caused to levitate a spinning magnetic top made of a flat ring magnet, a nonmagnetic spindle and one or more nonmagnetic weights for adjusting the mass and therefore the height of levitation of the spinning magnetic top. For a substantially uniformly magnetized base or shell it was explained in our prior application that the outer periphery of the base or shell affects the stability of a levitation system incorporating the shell. In particular, a shell having a polygonal shaped periphery has a region a few centimeters above the surface of the shell and along the diagonals thereof where the magnetic field gradients are such as to provide both lifting and centering forces on a magnetic dipole (the spinning top) in that region. It was observed that non-polygonal peripheral shapes, such as circular and elliptical shapes, of a uniformly magnetized shell did not appear to provide the aforementioned region where both lifting and centering forces exist.
As was explained in our aforementioned prior application, now U.S. Pat. No. 5,404,062, the height at which the dipole magnet levitates can be increased by weakening the magnetic field at the geometric center of a polygonal (square) shell or base magnet. Such weakening can be accomplished by cutting a hole in the center of the shell magnet or by mounting a magnetic disk of opposite polarity over the geometric center of the base magnet.
It has now been found according to the present invention, that the outer periphery of the shell or base magnet need not be polygonal in shape if the magnetic field of the base magnet is made non-uniform by partial demagnetization in a central region of the base magnet. In other words, the outer periphery of the flat base magnet can be any shape, e.g., circular, elliptical, polygonal, if the magnetic field of the base magnet is partially demagnetized or weakened to some extent at or near a central region of the base magnet, preferably at or near the geometric center of the base magnet.
The magnetic field may be weakened by cutting a central hole in the base magnet or by mounting a smaller magnet such as a disk magnet of opposite polarity in a central region of the base magnet. It is preferred, however, to weaken the magnetic field of the base magnet by applying a strong magnet field of opposite polarity, e.g., with an electromagnet or permanent magnet, to a central region of the base magnet to permanently weaken or partially demagnetize a portion of the central region.
In addition to making possible the use of a base magnet having virtually any peripheral shape, the present invention also causes the levitated spinning dipole (top) to float or levitate at a greater height than for a uniformly magnetized base.
Furthermore, it has been found that the top is more easily spun when the magnetic field of the base is weakened.
A further feature of the method of the invention is the use of controlled partial demagnetization or weakening of the magnetic field in the central region of the base magnet to xe2x80x9ccalibratexe2x80x9d the levitation device by making the spinning top more stable. This feature, together with the adjustment of the weight of the spinning top, can be used to achieve an easily spun top which levitates in a relatively stable position for several minutes.
Still another feature of the invention is the use of small wedges or shims to adjust the position of the magnetic field of the base magnet with respect to the local vertical. This position adjustment helps to stabilize the levitation of the spinning magnet above the base magnet.